Recently, inkjet printers have become popular rapidly, because of their advantageous points, for example, of low noise properties, and low running cost. Also, color inkjet printers which enable printing on plain paper have been actively brought into the market. However, it is difficult to satisfy all the properties required for recording ink used for such inkjet recording system, such as color reproducibility, abrasion resistance, durability, light resistance and quick drying properties of a printed image, and letter bleeding (feathering), color boundary bleeding (color bleeding), double sided printing properties, and discharge stability of recording ink, and thus an ink is selected depending on the properties given priority according to the application, under present circumstances.
In most cases, an inkjet recording ink contains water as the main component and contains a wetting agent such as glycerin, and a colorant. As the colorant, dyes and pigments are mainly used. The dyes are excellent in color developing ability and storage stability but have a drawback that they are poor in light resistance, gas resistance and water resistance. In contrast, pigments are excellent in light resistance, gas resistance and water resistance, but have a drawback that they are poor in color developing ability.
Further, a dye ink using a dye as a colorant has a problem that it easily spreads on paper such as plain paper, and how to reduce bleeding (color bleeding) particularly in a boundary between a black ink and a color ink has become a problem to be solved.
As a solution to the color bleeding, there is a method of increasing the permeability of a color ink to paper higher than that of a black ink, to thereby prevent the black ink from penetrating a region of the color ink of a printed image. An attempt is made to solve the problem with color bleeding by adding a surfactant to the ink composition and adjusting the amount of the surfactant, however, a reduction of color bleeding by dye inks has not yet been made as efficient as pigment inks are. Also, there is a method to suppress the permeability of a color ink by increasing the viscosity of the black ink, however, since there is an upper limit to the viscosity for stably discharging the ink in an inkjet recording system, a sufficient effect has not yet been obtained.
PTL 1 discloses an ink set in which the amount of a water-soluble solvent is greater than that of water, and both a black ink and color inks contain the water-soluble solvent in an amount greater than that of water. However, the ink has a problem that color bleeding is easily caused between the black ink and the color inks.
An ink which is monochrome and contains a water-soluble solvent in an amount greater than that of water is described in PTLs 1 to 5 and the like, but these inks do not take the color bleeding into account.